1. Field of the Invention
The present invention relate to a data driver for use in a liquid crystal display and, more particularly, to a ramp signal application type of data driver.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating a construction of a conventional data driver. FIGS. 2A to 2C are timing diagrams illustrating output states at point. A, B and C of FIG. 1. Referring to FIG. 1, the conventional data driver includes a plurality of registers 1, a plurality of counters 2 and a plurality of pass transistors 3. Digital data is sequentially loaded into the plurality of registers 1. After the digital data is loaded into a register it is transferred to a corresponding counter 2.
When a load signal is applied to the lead line of each of the counters 2, the counters 2 each set a corresponding digital data count value and count down from the digital data count value according to an input clock signal. The counters 2 execute a logical ORing operation on signals output from a plurality of internal flip-flops, to thereby produce a pulse width modulated output. Output digital bits from the counters 2 are applied to corresponding pass transistors 3 for producing ramp signal for producing ramp signal lines.
When a load signal is applied to the lead line of each of the counters 2, the counters 2 each set a corresponding digital data count value and count down from the digital data count value according to an input clock signal. The counters 2 execute a logical Oring operation on signals output from a plurality of internal flip-flops, to thereby produce a pulse width modulated output. Output digital bits from the counters 2 are applied to corresponding pass transistors 3 for producing ramp signal lines.
When the output digital bits from the counters 2 become high, xe2x80x9cHxe2x80x9d level, the corresponding pass transistors 3 are turned on, and the ramp signals are applied to data lines.
On the other hand, when the output signals from the counters 2 become low, xe2x80x9cLxe2x80x9d level, the corresponding pass transistors 3 are turned off and the ramp voltage on the data lines is unchanged. The ramp voltage determines a brightness of picture elements in a liquid crystal display.
FIG. 2A is a timing diagram showing output waveforms of the applied ramp signal. FIG. 2B is a timing diagram showing output waveforms of a counter 2 in the case of digital data xe2x80x9c000010xe2x80x9d and xe2x80x9c111101xe2x80x9d. FIG. 2C is a timing diagram showing output waveforms of a voltage or responding to a transformed ramp signal of FIG. 2A in response to digital data output of the counter 2 of FIG. 2B.
FIG. 3 is a circuit diagram of the counter 2 of FIG. 1. A load signal is inverted and applied to xe2x80x9cORxe2x80x9d gate 300, digital data, data A-D, is supplied to each terminal of the counters 2 through xe2x80x9cANDxe2x80x9d gates 310. Next, the counters 2 are each set to a corresponding data count value of the applied digital data. After the data loading is completed, a clock signal is applied to flip-flops 312-318 in counter 2. The counters 2 respectively countdown by 1 from the digital data count value, and when the digital data value is xe2x80x9c0000xe2x80x9d, the counter is reset and halted. Then, OR Gate 320 performs a logical OR operation on the flip-flop outputs QA, QB, QC and QD. The counters 2 respectively output the OR-ed result as an output signal.
Accordingly, the conventional data driver for use in a liquid crystal display requires counters with complicated circuit construction.
Accordingly, the present invention is directed to a data driver for use in a liquid crystal display that has a simplified structure.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a data driver in a liquid crystal display, the data driver including a plurality of data lines; a plurality of shift registers for sequentially outputting a sample control signal; a plurality of sample and hold circuits, connected to each of the data lines, for sampling data on corresponding data lines in response to the sample control signal; and a plurality of timing control parts for receiving sampled data from the sample and hold circuits and for performing a logical operation on the sample data.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.